As the feature size of the semiconductor device is becoming increasingly small and the transistor has become three-dimensional, two dimensional characterisation, such as, width and Line Edge Roughness (LER) is no longer sufficient for characterizing these devices. Characteristics based on the three dimensional nature of the device, such as, height, Sidewall Roughness (SWR) and Sidewall Angle (SWA) are increasingly important metrics for these metrology applications. However, it is becoming increasing difficult for current metrology technologies to provide the required three dimensional information about such small structures.
The Atomic force Microscope (AFM) has been widely used for research purposes, and it has also been used in the industry as a metrology tool. One of the main applications of the AFM in metrology is height measurement. However, because most AFMs operate in a top-down configuration, the AFM has limited access to the sidewall of a trench or other structure. This is especially true when the sidewall angle is close to, or greater than 90 degrees. This can be addressed by using novel probe designs and incorporating some degree of lateral motion in the probe tip using piezoelectric actuators or by torsionally vibrating the probe. However this lateral motion may be too slow for in-line metrology applications.